The present day danger to doctors, medics and nurses resulting from using syringes is well known. But to a subsequent user, contagious diseases such as AIDS and hepatitis have made the reuse of a syringe a catastrophic event. Yet notwithstanding all of these dangers and problems, the common syringe that has been sold for years and is still used in volume, remains the same. While this syringe may use a removable sheath, this does not effectively protect against inadvertent needle pricks, that often occur in just trying to return a used hypodermic needle to the sheath. Also sheaths do not protect against the dangerous and highly injurious reuse of hypodermic needles.
There are syringe designs that have the capability of retracting the needle or the needle holder into the syringe barrel, as exemplified in U.S. Pat. Nos. 4,838,870 and 4,650,468 that retract the needle into the barrel, and in U.S. Pat. Nos. 4,747,830 and 4,790,822 that retract the needle holder into the syringe barrel. The latter U.S. Pat. Nos. 4,747,830 and 4,790,822 additionally disclose breaking off the end of the plunger shaft and holding the needle and holder in the barrel.
The approach of retracting the needle or the needle housing into the syringe barrel has theoretical advantages. But in actual use the designs disclosed in the aforesaid patents have proven to be impractical in operation, are not cost effective as they are expensive to manufacture, and present problems in leaving substantial amounts of fluid in the barrel after the needle or needle holder have been retracted. Further the differences in the operation of the new designs relative to the old common syringe are so great that the safety factors achieved are not sufficient to justify their adoption.
The patents disclosing withdrawing the needle into the barrel have very complex mechanisms that have the disadvantage of being costly to make and are basically impractical in operation. The mechanisms within the barrel volume for grasping and retracting the needle are so bulky it is difficult to sufficiently eject the fluid from the syringe barrel. So in retracting, substantial amounts of liquid are left in the barrel to leak out later. Even if this liquid is retained in the barrel, this still leaves the syringe in a less desirable condition for disposal. Essentially a syringe is a very simple device and it has to be kept simple in construction and in operation as well as being inexpensive to make; or it will not achieve wide acceptance because of the large number of syringes that are used each year.
The patents that disclose retracting the entire needle holder and needle into the barrel, likewise have very complex mechanisms for accomplishing the retraction that makes such syringes expensive to make and subject to operation failure. Some of these systems require that the forward end of the syringe be frangible. These syringes all are either not capable of being manufactured at a reasonable cost or cannot be broken easily. Further the frangible section makes the syringe structurally weak at a very critical point, and also makes the syringe unsealable after being broken. Some of these systems also require that the plunger shaft be broken to render the syringe inoperable and to assure that the syringe needle and holder cannot be pushed back out of the forward end of the barrel. The problem with this is that the plunger shafts are difficult to break in practical use. Even if the shaft can be broken, the effort in doing so is distasteful to the syringe user, because the syringe user has to be mindful of the fact that the unattached needle and needle holder can be caused to eject from the syringe barrel and cause an accidental pricking by the hypodermic needle. Further in the systems that retract the needle and holder into the barrel, after such retraction the barrel is essentially not closed at one end. So the fluid is released, making an obvious mess. The two systems design that retract the needle and holder into the barrel have a design that makes the syringe expensive and complex to make, and so the price and complexity makes the syringe design unlikely to be used in the future.
There is therefore, a real and demanding need for a new and improved syringe that easily, quickly and positively retracts the needle and needle holder into a sealed condition within the syringe barrel, which has a means for easily breaking off the shaft from the piston rendering the syringe incapable of future use, and for providing a simple and easy means of sealing the open forward end of the syringe in locked manner so that the syringe needle and holder cannot inadvertently escape or be jarred out of the open end of the syringe barrel, and that provides a new and improved syringe that is relatively inexpensive to make, is simple and positive in operation, that is safe and easy in use, that allows maximum ejection of the fluid from the barrel in use, that locks the needle holder from being inadvertently withdrawn into the barrel, that retains the retracted syringe in the barrel and seals the syringe and the fluids in the barrel, and that can be disposed of in the sealed condition.